KB, MB, pixels, DPI and cm: what they mean on a form
KB and MB measure file size. Pixels measure a picture's width and height. DPI says how many pixels print in one inch. To turn centimetres into pixels, divide by 2.54 and multiply by the DPI: 3.5 × 4.5 cm at 300 DPI is 413 × 531 pixels.
Updated · by the Resize Baba team
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File size: KB and MB
File size is how much storage the file takes. A phone photo may be 3 MB. Forms often allow only 20 to 200 KB, so the photo has to be compressed.
Some portals count 1 KB as 1,000 bytes and others as 1,024. A file that is just under the limit by one method can fail the other, so aim a little inside the limit.
Pixel size
Pixels are the dots in a picture. '200 × 230 px' means 200 wide and 230 tall. A form that asks for exact pixels will reject a file with different dimensions, even if the KB is right.
DPI
DPI (dots per inch) only matters for printing. It does not change how sharp a picture looks on screen. A 1200 × 1800 px photo prints 4 × 6 inches at 300 DPI.
If a form says 'at least 300 DPI' and gives pixel sizes, matching the pixels is what matters; the DPI value in the file can be set to 300.
Centimetres to pixels
Pixels = centimetres ÷ 2.54 × DPI. For 3.5 cm at 300 DPI: 3.5 ÷ 2.54 × 300 = about 413 pixels. Resize Baba's Custom size has a helper that does this for cm, mm and inches.
Questions people ask
How many KB is 1 MB?
1 MB is 1,000 KB, or 1,024 KB by the older binary convention.
Does changing DPI make a photo sharper?
No. DPI only changes the print size. More detail needs more pixels.
What is 35 × 45 mm in pixels?
At 300 DPI, 413 × 531 pixels.